1. Field of the Invention
The invention relates to a bearing structure, and more particularly, to a C-type bush that an included angle between the opening and the center of a circle of the guiding rod is less than 180 degrees.
2. Description of the Prior Art
The optomachinery used for scanning images usually has a bush, and the bush slides along a guiding rod to scan images, so the bush is a main guiding interface for transmission and is a controlling element of precision. FIGS. 1(a)–1(c) are diagrams of three bushes according to prior art. The optomachinery slides along a guiding rod 12 with a bush 10, the bush 10 is usually made with a lubricative material. The bush can be a single-element type as FIG. 1(a) shows, or a multi-element type as FIG. 1(b)(C) show.
In contrast to the bush 10 showed in FIG. 1(b) and FIG. 1(c), the bush 10 in FIG. 1(a) has an advantage of fewer parts, but has disadvantages of larger capacity and accumulative tolerance for integral parts. Thereinafter is explained with FIGS. 2(a) and 2(b). FIG. 2(a) is a diagram shows the conventional single-element bush 10 installed in the optomachinery 14, wherein the distance L between the center of the guiding rod 12 and the housing 16 is:L=a+b+c+dwherein a is the radius of the guiding rod 12;                b is the thickness of the bush 10;        c is the thickness of the bearing component 142 of the optomachinery 14;        d is the distance between the optomachinery 14 and the housing 16.In which the optomachinery 14 is a movable device, the configuration of distance d is necessary. Since L is composed of four parameters, the accumulative tolerance depends on four tolerances.        
FIG. 2(b) shows another bearing structure using the convenient single-element bush. The bearing component 142 of the optomachinery 14 has an opening, and the distance L between the center f the guiding rod 12 and the housing 16 is:L=a+b+cwherein a is the radius of the guiding rod 12;                b is the thickness of the bush 10;        c is the distance between the bush 10 and the housing 16.In which the bush 10 is combined and moved with the optomachinery 14, that is to say the bush 10 and the optomachinery 14 are movable devices, and the configuration of distance c is necessary. In this bearing structure, since L is composed of three parameters, the accumulative tolerance depends on three tolerances, and the size of the optomachinery and the accuracy cannot be improved.        
Another conventional bush is developed to overcome the problem of size, as FIGS. 3 and 3(a) show. The bush 10′ is U-type designed and contacts the guiding rod 12 in semicircle. The bush 10′ cannot be fixed on the guiding rod 12 without a wear-resisting device or a lubrication device 18. The bush 10′ must cooperate with the lubrication device 18 holding the housing 16 or the glass so that the optomachinery 14 can stably slide along the guiding rod 12. However, the design of the wear-resisting device or the lubrication device 18 not only occupies more space but also increases assembly and making cost. Furthermore, while actually operating, the contact between the bush 10′ and the guiding rod 12 is only in few points, the inner surface of the bush 10′ will be damaged after long time using and cannot firmly fix on the guiding rod 12. This will cause the optomachinery 14 wavering while moving.
In addition, the Taiwan patent publication number 465885 “A bush apparatus of scanner” discloses a bush apparatus similar to the single-element type bush in FIG. 1(a). The disclosed characteristic is designing the assembly structure, and cannot solve the problems of size and accumulative tolerance.
The claimed invention provides a bush and a bearing structure applied thereof to fit in with the requirement for small size optmachinery and improve the assembly accuracy.